In certain applications of broadcast television, CATV, and the like it is desirable to present to a viewer simultaneously multiple television presentations for selective viewing. These multiple presentations can be broadcast by conventional broadcast channels or via CATV. Alternatively, it is desirable to record two television programs in real time on a single track of a video tape recording for selective viewing upon playback.
Prior to the present invention this could only be accomplished by assigning the multiple presentations different areas of the television screen and selectively unblanking a particular selected area. This arrangement is not completely satisfactory in that the selected presentation is relatively small in size.
Furthermore, when substantial areas of the screen are blanked and, thus, substantial areas of black or white are presented to the TV receiver, the average level of signal presented to the receiver is appreciably different from a normal signal. This can interfere with the AGC circuitry of both the studio camera and the receiver. This interference can be sufficient to cause display of the information in the blanked areas although at a low level thus defeating the very intent of the dual presentation.